Electrical resistance device



rneniod'reb. la, 193s UNITED `s'l'ii-'lrzs PAT-snr oFFlcE ELECTRICALassis'rmcn nmol 7 Y' Willy Dumke, Chicago, Ill., aaaignor 'to Utah RadioProducts Company,

poration of Illinois Application July 9,1932, Serial No. 021,0 I

1o claims, (cl. soi-w having a flexible contact member of novelconstruction interposed therebetween for preventing wear on theresistance element or distortion of the resistance curve.

a flexible contact member' which is electrically independent of theresistance element at all times except at one point which may beoptionally varied throughout the entire range of said element.

' More specifically stated, an object is to provide a resistance elementof cylindrical' shape havingv theexposed surface of the resistanceelement in-. wardly presented and opposed by a flexible member which ismaintained normally in insulated and spaced relation and which iscapable of being variably contacted with the exposed surface, said4parts having a novel arrangement which facilitates the connectionsthereof with the required terminals.

Another object is to provide a novel flexible contact member for aresistance element of this nature.

Other objects and advantages will become apparent in the followingdescription -and from the accompanying drawing, in which: y

Figure 1 is anopen face view of a device em` bodying the features of theinvention.

m. 2 is a sectional view through o. portion of `the device taken asindicated by the line 2-2 of Fig. 3, parts being broken away to clarifythe muon. Fig. 3 is a central section through the device on the line 8 3of Pig. 1.

m. 4 is nii-elevation or tno inferior of uio aovioe looking at theterminal assembly,

omittedfor better disclosure.

Fig. 5 is a fragmentary sectional view on an enlarged scale takenthrough one side of the device.

ngisafragmentaryplanviewonareduced have shown in`,the drawing and willharem describe in detail the'preferred embodiment. but it is to be'understood that l do not thereby intend to limitthe invention to thespecific form disclosed-but intend to cover all modifications andalternative constructions falling within the spirit and scope of theinvention as expressed in the appended claims.

Referring to the drawing, wherein the preferred embodimentof therinvention is shown 10 merely for the purpose of illustration; Il desig-I nates generally an enclosing case or which is preferably formed ofsheet metal Aor economy inv manufacture. The case is; cup-shaped and.comprises a base I I and a substantially cylindrical 15 A furtherobject resides in the provision of such side wall I2. defining an openface which is normally closed by a suitable cover I2* (Eig. 3) which fis heldin place by tabs Il. 'Ihe base is apertured as at Il (Fig. 4) vtoreceive a bushing il (Fig. 3) of conventional construction within whichis iour- 20 naled a shaft il arranged to be rotated by a' well-v knowntypeof knob or nnger piece I'i.- Theshaft I8 supports a presserassembly. generally indicated at il, the purpose of which will beherein.- after more fully described.

. Adiacent the inner surface of the side wall i2 is a sheet I! of anysuitable insulating material, which preferably covers the entire wallsurface. A fiat annular ring or washer Il, also of insulating material,covers a substantial portion of the 30 base of the case inwardly of saidwall. An annular cylindrically shaped resistor 2| is disposedconcentrically and interiorlyofY the sheet of insulating material Il butdoes not extend completely through the'length of the inner periphery 35of the While'any suitable type of resistor y v .may be employed. thatwhich is preferred comf prises a smooth surface resistor element!! (Fig.'5) .of graphite or like material mounted on or carried by a somewhatflexible base of a phenol 4o lcondensation product 23 or similarmaterial. The --exposed surface of the resistor element is ar- V by therelatively movable contact usually em- 4s ployed, a flexible contactmember is provided in interposed relation between the presser assemblyand the resistor element. With particular reference to Figs. 4,-5 and 6,a preferred fonn of con tact member comprises imelongated strip 24 -cf50 thin, nexible.- current conducting material. suchasbronae,whichstripisdisposedwithinandadiacenttotheexpcsedsinfacecftllereaistorele-` ment l2.

" The flexible strip 24 is preferably maintained as in definitely spacedand concentric relationship to the resistor element in the followingmanner (see Fig. 6). From one side of the strip relatively narrow webs2l extend, each of which terminates in a ilat plate 28. The strip 24,webs 25 and plates 28 are dimensioned so that. by bending the webs alonga longitudinal line, generally indicated by the line A-A in Fig. 6,adjacent the plates, a structure of generally U-shaped cross section maybe obtained which will flt about or straddle the inner side edge of theresistor 2|. Thus.. the strip 24 may be maintained in deflnitely spacedrelationship to the resistor element 22 by means of the webs and plateswhich are bound between the resistor 2| and the insulating sheet. I9 andring 2|). The plates 26 preferably have avrelatlvely large surfaceareavto securely hold the strip 24 in place and, while the platesv mightbe formed as a continuous st rip, it is preferred to employ, plates sothat the U-shaped structure may most readily follow the kcurvatureof thecase.

' As maybe seen in Fig. 5, the resistor element 22 preferably stopsshort, as indicated at-21, of the inner side edge of the resistor 2| toinsulate vthe resistor element from the contact strip. Prei'- erably. anannular relatively narrow ring 28 of insulating material is 'interposedbetween vthe webs 2l and the resistor element 2l adjacent the innerlportion of the element. This ring definitely maintains the spacedrelationship between the strip 24 and the resistor element. l

t The presser assembly Il embodies a dat plate 29 which is rigidlysecured to the shaft 'I6 for I `rotation therewith. The plate extendsradially of the shaft to a point substantially adjacent tothecontactstrip Mandisthereprovidedwithan outwardly urged presser shoeIB. The shoe carries a tip 2| of insulating material which engages thecontact strip :24 and pressessaid `strip into engagement with theunderlying surface ofthe resistor element 22 as shown in Figs. 1 and 3.'I'he point of contact between the strip and resistor element may,therefore, be'varied by infinitemmal degrees ,or steps throughout theentire length of the resistor by manipulation of the knob I1.

As has been mentioned, the resistor does not completely encircle theinterior of the case and a terminal I2 is provided for each end of theresistor. These terminals comprise flat plates l! (Fig. 4) arranged tooverlie and contact the surface of 'the resistor element 22 at the endsof the resistor and have angularly extending contact fingers 34 (Figs.land 2) which extend through small slots Il 4in the insulating sheet Iland an elongated' slot Il in the case wall I2. A third; terminal 31 of'somewhat similar constructiony is interposed between the' two resistorterminals I2 andV is electrically insulated from said terminals betweenthe ends 38 (Fig. 2) of the resistor, which ends extend beyond theterminals 32 to position the back side thereof in overlying relation tothe terminal Il.V`

Both ends of the contact strip 24 are prefer' ably connected to thethird terminal 81. 1 This may be accomplished in a simple manner byforming tabs 3l (Fig. 6) 'to extend longitudinally from thecontact'element and preferably from i within the case and the electricalconnections with the several terminals may be effected and maintainedbya single. insulated', securing means.

Thus, as shown in Fig. 4', the middle terminal 31 has an enlargedcentral aperture or recess 4l) formed therein and the wall of the case,together with the insulating sheet I9 opposite this recess, isapertured. as at 4i, to receive a screw 42 (Figs. 1, 2 and 3) whichextends vinto screw threaded engagement with an arcuate plate 43. Theplate 48 extends laterally to overlie both of the outer termiials 32 anda sheet of insulation 44 is interposed between the plate and thetermlnals.` As is shown clearly in Fig. 4, the recess 4l is considerablylarger than the screw to prevent short circuiting of the terminal VBIthrough the screw. Thus. by the screw 42 and plate 4l, the terminals 32may be drawn tightly into electrical contact with the underlying ends ofthe resistor 2| thereby pressing the back side of each end of theresistor against the. opposite sides of the middle terminal I1 tobindthe tabs I9 against the terminal 31.

It will be seen from the foregoing description vthat a device has beenprovided wherein the sembly and the rotating shaft therefor areelectrically independent of the current carrying elements. Hence, thedevice is capable of carrying an yexceedingly heavy overload of -currentwithout danger. A furtherimportant advantage is that the enclosingmetallic case and cover, which are electrically independent of allcircuits, provide s. static shield about the device to suppress oreliminate interference. The preferred manner of mounting the contactelement in place and of maintaining said element In definitely spacedrelation to the resistor facilitates assembly of these parts and resultsinl a structure which is inherently sturdy.

I claim as myV invention:

l. An electrical resistance device comprising, in combination. `i.cylindrically shaped insulator having a resistance element on the innerperiphery thereof, an annular contact member disposed in opposition tothe inner exposed face of said resistance element, an insulating stripextending along the length of said contact memberbetween a part of saidmember and the. face of said resistance' element to normally maintainsaid contact member from end to end in radially spaced vrelation to saidresistance element, said contact member being movable radially intocontact with said element. and means movable circumferentiallynrelativeto said insulator and cooperating with the part of said contact memberwhich i: free of said insulating strip for movingl saidpari intoengagement with said element at variable points along the lengththereof.

' 2. An electrical 'resistance device comprising in combination, acylindrically shaped insulatoi having a resistance element on the innerperiphery thereof, an annular contact member disposed in opposition tothe inner exposed face oi said resistance element, means disposed atspaced points longitudinally of said member for maint taining saidmember `normallyin radially spaces tosaid. element, said contact membbeing movable radially outward int'o contaoi with said element. `meansmovable circumferen- -tlally relative to said insulator andcooperatingwith said contact member for moving said member intoengagement with said element at variable points along the lengththereof, and meansl for connecting said device in an electrical circuitincluding a separate lterminal electrically connected with said contactmember.

3. An electrical resistance device comprising,

.in combination. a cylindrically shaped insulator having a resistanceelement on the inner periphery thereof, anl annular contact memberdisposed in opposition to the inner exposed face of said resistanceelement an'd normally 'maintained in' radially spaced relation thereto,said contact member being movable radially into contact with saidelement. means movable circumferentially relative to saidv insulator andcooperating with said contact member for moving said member intoengagement with said element at variable points along 'the lengththereof, and means inter#l posed between apart of said contact memberandsaid element and vextending substantially along the lengththereof fornormally spacing the one from the other.

" 4. An electrical resistance device comprising.

in combination. a cylindrically shapedelement presenting an inwardlyfacing resistor, an annular flexible contact member within'said elementand concentrically disposed with respect to said reof the resistorbetween said resistor and element and a supporting portion positionedopposite the other face of the resistor for supporting the iirstmentioned portion in normally spaced relation to-said resistor.

6. An electrical resistance device comprising, in

combination, a case having a cylindrical side wall, a resistor mountedwithin said side wall and facing inwardly of the case,` means forinsulating said resistor from said case.- a contact Amember disposed insubstantially coextensive andinor- Vmally spaced relation to saidresistor and including a supporting part held between said resistor andthe case. means for insulating said `contactfinember trom'the resistorand the case.

and presser means supported on said case for engagement with saidcontact member and movable to eilect a variable 'contact of said contactmanner and and resistor.

. '1. An electrical resistance device comprising, in

combination, a case having a cylindrical side wall,

a resistor mounted within said side 'walland facing inwardly of thecase, means for insulating said resistor from said case; acontact'element disposed in substantially coextensive and normallyspaced relation to said resistor and including a supporting partextending between the opposite side ot the resistor and the's'ide wall.meansfor insulating said contact element from. the resistor and thecase, and rotatable means Journaied on the case and engaging saidcontact member to press the member into contact with the resistor atvariable points.

An electrical resistance device comprising. in combination, a casehaving a cylindrical side w'all, a cylindrical insulating base having 'asmooth surfaced resistor disposed on the inner periphery' thereof anddimensioned to fit'within the-case, a contact member of generallyU-shapecross sectionv arrangedto nt about the inner side edge of said base andincludinga continuous contact strip, adjacent to and substantiallycoextensive with said resistor, insulating means separating the contactmember from said case and said resistor, a terminal. connectedwith eachend ofV said resistor, a separate terminal connected with both ends ofsaid contact member, and means for variably pressing said contact stripagainst the resistor. 1

combination, a case having a cylindrical side wall,

a cylindrical insulating base having a smooth surfaced resistor disposedon the inner periphery thereof 'and dimenslonedto flt within the sidewall, insulating means between the resistor and the case, a contactmember of generally U-shape cross section arranged to fit about theinner side edge voi.' said base and including a continuous contact stripadiacent to and substantially coextensive with said resistor, insulatingmeansl separating the contact member from said re'-v sistor, insulatedmeans for variably pressing said contact strip against the resistor,spaced termman disposed one'at each end of the resistor beyond the endsof the contact strip and in over'- lying relation to the resistor, athird terminal positioned intermediate the rst vmentioned ter-- minals,said contact member having an extension at each end behind the base forconnection with said third terminal, and insulated means for securingsaid parts in place.

10. A flexible contact member foran electrical resistance device of thecharacter described comprising. in combination, an elongated stripconstituting the contacting part of the member, a

'plurality of separate elements for support of the vcontacting part inassembly, and connections intermediate said elements and-strip adaptedfor bending to provide astructure of generally Uf so shaped crosssection.

1 z WILLY DUMKE.

. an 9. An electrical resistance device comprising, 'in

